Lubricating Oil Composition for Internal Combustion Engine

ABSTRACT

The present invention provides a lubricating oil composition for an internal combustion engine, comprising: a lubricating base oil; an ashless friction modifier; and a boron-containing dispersant.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition for an internal combustion engine.

BACKGROUND ART

In recent years, improvement in fuel economy is required for lubricating oils used for internal combustion engines such as vehicle engines (engine oils) to reduce CO₂ emission from vehicles. Although reduction in the viscosity of oils is mentioned as a method for improving the fuel economy of engine oils, engines may be worn when the viscosity is reduced excessively. Therefore, methods for improving fuel economy by adding a friction modifier have been examined instead.

For example, a diesel engine oil composition containing a predetermined mineral base stock and various additives such as a molybdenum dithiocarbamate for improving fuel consumption by reducing friction is disclosed in Patent Literature 1.

CITATION LIST Patent Literature

[Patent Literature 1]

Japanese Patent Application Publication No. 2002-220597

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a lubricating oil composition for an internal combustion engine, that is good in fuel economy and also corrosion protection of copper and lead.

Solution to Problem

The present invention provides a lubricating oil composition for an internal combustion engine, comprising a lubricating base oil, an ashless friction modifier and a boron-containing dispersant.

A lubricating oil composition further comprises an overbased organic acid metal salt that is overbased with preferably calcium borate.

A lubricating oil composition is preferably used as a diesel engine oil.

Advantageous Effects of Invention

According to the present invention, a lubricating oil composition for an internal combustion engine, that is good in fuel economy and also corrosion protection of copper and lead can be provided.

DESCRIPTION OF EMBODIMENTS

A lubricating oil composition according to this embodiment comprises a lubricating base oil, (A) an ashless friction modifier (also called “(A) component” hereinafter), and (B) a boron-containing dispersant (also called “(B) component” hereinafter). The lubricating oil composition according to this embodiment is preferable as a lubricating oil composition for an internal combustion engine.

The lubricating base oil is not particularly limited and may be a base oil that is used for common lubricating oils. Specific examples of the lubricating base oil include mineral base stock, synthetic base oils and mixtures of both types.

Examples of the mineral base stock include paraffinic, naphthenic and other mineral base stock, which are refined by subjecting a lubricating oil fraction obtained by distilling crude oil under atmospheric pressure and vacuum pressure to one of refining treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing and clay treatment, or to two or more thereof combined properly, and also normal paraffins and isoparaffins. One of these mineral base stock may be used alone, or two or more thereof may be used in combination at any proportion.

Examples of preferable mineral base stock include the following base oils:

-   (1) A distillated oil by the atmospheric distillation of a     paraffinic base crude oil and/or a mixed base crude oil; -   (2) The whole vacuum gas oil (WVGO) of a vacuum distillate of the     atmospheric distillation residue of a paraffinic base crude oil     and/or a mixed base crude oil; -   (3) Wax obtained by a step of dewaxing a lubricating oil, and/or     Fischer Tropsch wax produced by a GTL process or the like; -   (4) A mild hydrocracking treatment oil (MHC) of one selected from     the above (1) to (3) or a mixed oil of two or more selected     therefrom; -   (5) A mixed oil of two or more oils selected from the above (1) to     (4); -   (6) The deasphalted oil (DAO) of the above (1), (2), (3), (4), or     (5); -   (7) The mild hydrocracking treatment oil (MHC) of the above (6); and -   (8) A lubricating oil obtained by using a mixed oil of two or more     oils selected from the above (1) to (7), or the like as a raw oil,     refining this raw oil and/or a lubricating oil fraction collected     from this raw oil by a common refining method, and collecting a     lubricating oil fraction.

In this description, the common refining method is not limited, and any refining method used at the time of producing base oils can be adopted. Examples of the common refining method include the following refining methods:

-   (a) Hydrorefining such as hydrocracking or hydrofinishing; -   (b) Solvent refining such as furfural solvent extraction; -   (c) Dewaxing such as solvent dewaxing or catalytic dewaxing -   (d) Clay refining by acidic clay, active clay or the like; -   (e) Chemical (acid or alkali) refining such as sulfuric acid washing     or caustic soda washing.     One of these refining methods can be used alone, or two or more     thereof can be used in any combination and any order.

Examples of the synthetic base oils include poly-α-olefins or hydrogenated products therefrom, isobuten oligomers or hydrogenated products thereof, isoparaffins, alkylbenzenes, alkylnaphthalenes, diesters (ditridecyl glutarate, di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, di-isodecyl adipate, ditridecyl adipate, di-2-ethylhexyl sebacate and the like), polyol esters (trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, pentaerythritol pelargonate and the like), polyoxyalkylene glycols, dialkyl diphenyl ethers and poly-phenyl ether and the like, and the poly-α-olefins are particularly preferable. Examples of the poly-α-olefins include oligomers or co-oligomers of cc-olefins having 2 to 32 carbon atoms, preferably 6 to 16 (1-octen oligomers, decene oligomers, ethylene-propylene co-oligomers and the like), and hydrogenated products therefrom. One of these synthetic base oils may be used alone, or two or more thereof may be used in combination at any proportion.

The kinematic viscosity at 40° C. of the lubricating base oil is preferably 13.0 mm²/s or more, more preferably 15.0 mm²/s or more, and further more preferably 17.0 mm²/s or more in view of oil film formation becoming enough, better lubricity, and the evaporation loss becoming lower under high temperature conditions. The kinematic viscosity at 40° C. of the lubricating base oil is preferably 42.0 mm²/s or less, more preferably 40.0 mm²/s or less, and further more preferably 38.0 mm²/s or less in view of providing improved low-temperature viscosity characteristic and better fuel economy.

The kinematic viscosity at 100° C. of the lubricating base oil is preferably 2.0 mm²/s or more, more preferably 3.0 mm²/s or more, and further more preferably 3.5 mm²/s or more in view of oil film formation becoming enough, better lubricity, and the evaporation loss becoming lower under high temperature conditions. The kinematic viscosity at 100° C. of the lubricating base oil is preferably 8.0 mm²/s or less, more preferably 7.0 mm²/s or less, and further more preferably 6.0 mm²/s or less in view of providing improved low-temperature viscosity characteristic and better fuel economy.

The viscosity index of the lubricating base oil is preferably 100 or more, more preferably 110 or more, and further more preferably 120 or more in view of good viscosity-temperature characteristic, heat and oxidation stability, and volatilization prevention as well as much lower coefficient of friction. The viscosity index of the lubricating base oil is preferably 180 or less, more preferably 170 or less, and further more preferably 160 or less in view of the good low-temperature viscosity characteristic.

The kinematic viscosity and the viscosity index in the present invention mean a kinematic viscosity and a viscosity index that are measured on the basis of J1S K2283: 2000.

The content of the lubricating base oil may be, for example, 50% by mass or more, 70% by mass or more, or 90% by mass or more on the basis of the total amount of the lubricating oil composition.

(A) Examples of the ashless friction modifier include a nitrogen-containing ashless friction modifier and an oxygen-containing ashless friction modifier, and the nitrogen-containing ashless friction modifier is preferable. Specific examples of the (A) component include compounds such as amines, amides, imides, fatty acid esters, fatty acids, aliphatic alcohols, and aliphatic ethers. These compounds have, for example, at least one hydrocarbon group having 6 to 30 carbon atoms, preferably an alkyl group or an alkenyl group having 6 to 30 carbon atoms, and more preferably a linear alkyl group or a linear alkenyl group having 6 to 30 carbon atoms. The (A) component is preferably at least one selected from amines, amides and fatty acid esters, and more preferably at least one selected from amines and amides in view of the better fuel economy.

As the amines, linear or branched aliphatic monoamines or aliphatic polyamines, and alkylene oxide adducts of these are illustrated. These amines may have, for example, 6 to 30 carbon atoms. The amines are preferably amines represented by the following Formula (1).

R¹—NH₂   (1)

[In Formula (1), R¹ is a hydrocarbon group having 6 to 30 carbon atoms, preferably an alkyl group or an alkenyl group having 6 to 30 carbon atoms, and more preferably a linear alkyl group or a linear alkenyl group having 6 to 30 carbon atoms.] Specific examples of amines represented by Formula (1) include oleyl amine and stearyl amine.

As the amides, amides of linear or branched fatty acids and aliphatic monoamines or aliphatic polyamines are illustrated. These amides may have, for example, 7 to 31 carbon atoms. The amides are preferably amides represented by a following Formula (2).

R¹—C(═O)—NH₂   (2)

[In Formula (2), R¹ represents the same definition contents as the R¹ in Formula (1).] Specific examples of amides represented by Formula (2) include oleylamide and acrylamide.

As fatty acid esters, esters of linear or branched fatty acids and aliphatic monohydric alcohols or aliphatic polyhydric alcohols are illustrated. The fatty acids may be saturated fatty acids or may be unsaturated fatty acids. These fatty acid esters may have, for example, 7 to 31 carbon atoms. The fatty acid esters are preferably esters of fatty acids and aliphatic polyhydric alcohols, more preferably esters of linear fatty acids and aliphatic polyhydric alcohols, and further more preferably esters of linear unsaturated fatty acids and aliphatic polyhydric alcohols. These esters of aliphatic polyhydric alcohols may be complete esters, or may be partial esters, and are preferably partial esters. Specific examples of these esters of aliphatic polyhydric alcohols include glycerin monooleate.

The content of an (A) component is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and further more preferably 0.3% by mass or more on the basis of the total amount of the lubricating oil composition in view of the better fuel economy. The content of an (A) component is preferably 0.8% by mass or less, more preferably 0.7% by mass or less, and further more preferably 0.6% by mass or less on the basis of the total amount of the lubricating oil composition in view of the good long-term storage stability. The content of an (A) component is preferably 0.1 to 0.8% by mass, 0.1 to 0.7% by mass, 0.1 to 0.6% by mass, 0.2 to 0.8% by mass, 0.2 to 0.7% by mass, 0.2 to 0.6% by mass, 0.3 to 0.8% by mass, 0.3 to 0.7% by mass, or 0.3 to 0.6% by mass on the basis of the total amount of the lubricating oil composition in view of compatibility between fuel economy and long-term storage stability.

(B) Examples of the boron-containing dispersant include nitrogen-containing compounds such as succinimide, benzylamine, polyamines, and Mannich bases having an alkenyl group or an alkyl group derived from a polyolefin; and derivatives obtained by having a boron compound such as boric acid or a borate on these nitrogen-containing compounds. Among these, the derivatives obtained by having a boron compound such as boric acid or a borate act on these nitrogen-containing compounds are preferable. The above alkenyl group or alkyl group may be linear or branched and may be a branched alkyl group, a branched alkenyl group or the like derived from an oligomer of an olefin such as a propylene group, a 1-butene group or an isobutylene group, and a co-oligomer of ethylene and propylene.

Specific examples of the (B) component include modified succinimide obtained by modifying a so-called mono type of succinimide represented by a following formula (3) or a so-called bis type of succinimide represented by the following formula (4) with a boron compound such as boric acid and a borate.

In Formula (3), R² represents an alkyl group or an alkenyl group having 40 to 400 carbon atoms, and preferably represents an alkyl group or an alkenyl group having 60 to 350 carbon atoms. R² is preferably a polybutenyl group. m represents an integer of 1 to 5, and preferably represent an integer of 2 to 4.

In Formula (4), R³ and R⁴ are the same or different from each other, each represents an alkyl group or an alkenyl group having 40 to 400 carbon atoms, and preferably represents an alkyl group or an alkenyl group having 60 to 350 carbon atoms. R³ and R⁴ are each a polybutenyl group preferably. n represents an integer of 0 to 4 and preferably represents an integer of 1 to 3.

The content of the (B) component is preferably 90 ppm by mass or more, more preferably 100 ppm by mass or more, and further more preferably 110 ppm by mass or more in terms of a boron element on the basis of the total amount of the lubricating oil composition in view of the good corrosion protection of lead. The content of the (B) component is preferably 180 ppm by mass or less, more preferably 170 ppm by mass or less, and further more preferably 160 ppm by mass or less in terms of a boron element on the basis of the total amount of the lubricating oil composition in view of the good fuel economy. The content of the (B) component is preferably 90 to 180 ppm by mass, 90 to 170 ppm by mass, 90 to 160 ppm by mass, 100 to 180 ppm by mass, 100 to 170 ppm by mass, 100 to 160 ppm by mass, 110 to 180 ppm by mass, 110 to 170 ppm by mass, or 110 to 160 ppm by mass in terms of a boron element on the basis of the total amount of the lubricating oil composition in view of the compatibility between corrosion protection of lead and fuel economy at a still higher level. The content (in teems of boron element) of the (B) component can be measured by the ICP elemental analysis method.

The lubricating oil composition preferably further contains (C) an overbased organic acid metal salt overbased with calcium borate (also called “(C) component” hereinafter) in view of the better corrosion protection of lead. Examples of the organic acid metal salt include alkaline earth metal sulfonates, alkaline earth metal salicylates, alkaline earth metal phenates and alkaline earth metal phosphonates. The alkaline earth metal may be magnesium, calcium, and barium, and are preferably calcium. The (C) component is obtained, for example, by reacting the above organic acid metal salt; calcium hydroxide or calcium oxide; and boric acid or anhydrous boric acid.

The base number of the (C) component is preferably 50 mg KOH/g or more, more preferably 100 mg KOH/g or more, and further more preferably 150 mg KOH/g or more. The base number of the (C) component is preferably 500 mg KOH/g or less, more preferably 400 mg KOH/g or less, and further more preferably 300 mg KOH/g or less. The base numbers in the present invention mean base numbers measured by the perchloric acid method of 9. of JIS K2501: 2003.

The content of the (C) component is preferably 100 ppm by mass or more, more preferably 110 ppm by mass or more, and further more preferably 120 ppm by mass or more in terms of a calcium element on the basis of the total amount of the lubricating oil composition in view of the better corrosion protection of lead. The content of the (C) component is preferably 350 ppm by mass or less, more preferably 330 ppm by mass or less, and further more preferably 300 ppm by mass or less in terms of a calcium element on the basis of the total amount of the lubricating oil composition in view of the better corrosion protection of lead. The content of the(C) component is preferably 100 to 350 ppm by mass, 100 to 330 ppm by mass, 100 to 300 ppm by mass, 110 to 350 ppm by mass, 110 to 330 ppm by mass, 110 to 300 ppm by mass, 120 to 350 ppm by mass, 120 to 330 ppm by mass, or 120 to 300 ppm by mass in terms of a calcium element on the basis of the total amount of the lubricating oil composition in view of the better corrosion protection of lead. The content (in terms of calcium element) of the (C) component can be measured by the 1CP elemental analysismethod.

The lubricating oil composition may further contain other additives. Examples of other additives include a viscosity index improver, an antiwear agent, an antioxidant, an antifoaming agent, a pour point depressant, a corrosion inhibitor, an antirust, a demulsifier and a metal deactivator.

Examples of the viscosity index improver include a poly(meth)acrylate viscosity index improver, an olefin copolymer viscosity index improver and a styrene-diene copolymer viscosity index improver. These viscosity index improvers may be either non-dispersive or dispersive and is preferably non-dispersive. The viscosity index improver is preferably a poly(meth)acrylate viscosity index improver and is more preferably a non-dispersive poly(meth)acrylate viscosity index improver in view of highly improving effect on viscosity index as well as good viscosity-temperature, and low-temperature viscosity characteristics.

The pour point depressant may be, for example, a poly(meth)acrylate, and is a poly(meth)acrylate preferably the weight average molecular weight of which is 10000 to 300000 and more preferably the weight average molecular weight of which is 50000 to 200000.

Examples of the antiwear agent include phosphorous compounds such as phosphite esters (phosphites) and phosphate esters as well as these amine salts, metal salts and derivatives; and sulfur containing antiwear agents such as disulfides, polysulfides, sulfurized olefins, and sulfurized oils and fats.

Examples of the antioxidant include ashless antioxidants of phenols, amines and the like, and metal antioxidants of copper, molybdenum and the like. Specific examples of the phenol ashless antioxidants include 4,4′-methylene-bis-(2,6-di-tert-butylphenol) and 4,4′-bis-(2,6-di-tert-butylphenol), and specific examples of the amine ashless antioxidants include phenyl-α-naphthylamine, alkylphenyl-α-naphthylamines, dialkyldiphenylamines and diphenylamine.

Examples of antifoaming agents include silicone oils of which kinematic viscosity at 25° C. is 1000 mm²/s or more and 100000 mm²/s or less.; alkenyl succinic acid derivatives; esters of polyhydroxy aliphatic alcohols and long-chain fatty acids; and esters of methyl salicylates and o-hydroxybenzyl alcohol

Examples of the corrosion inhibitor include benzotriazole, tolyltriazole and imidazole compounds.

Examples of the antirust include alkenylsuccinic acid esters, polyhydric alcohol esters, petroleum sulfonate, alkylbenzene sulfonates and dinonylnaphthalene sulfonate.

Examples of the demulsifier include polyalkylene glycol-based nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers and polyoxyethylene alkylnaphthyl ethers.

Examples of the metal deactivator include imidazoline, pyrimidine derivatives, benzotriazole or derivatives thereof.

The content of other additives may be 0.01 to 20% by mass on the basis of the total amount of the lubricating oil composition.

The kinematic viscosity at 40° C. of the lubricating oil composition is preferably 31.0 mm²/s or more, more preferably 33.0 mm²/s or more, and further more preferably 35.0 mm²/s or more in view of the good lubricity. The kinematic viscosity at 40° C. of the lubricating oil composition is preferably 75.0 mm²/s or less, more preferably 72.0 mm²/s or less, and further more preferably 70.0 mm²/s or less in view of ensuring required low-temperature viscosity and further improving fuel economy.

The kinematic viscosity at 100° C. of the lubricating oil composition is preferably 5.0 mm²/s or more, more preferably 7.0 mm²/s or more, and further more preferably 8.0 mm²/s or more in view of the good lubricity. The kinematic viscosity at 100° C. of the lubricating oil composition is preferably 14.0 mm²/s or less, more preferably 13.0 mm²/s or less, and further more preferably 12.0 mm²/s or less in view of ensuring required low-temperature viscosity and further improving fuel economy.

The viscosity index of a lubricating oil composition is preferably 120 or more, more preferably 140 or more, and further more preferably 150 or more in view of good viscosity-temperature characteristic, thermal and oxidation stability and low volatility as well as much lower coefficient of friction. The viscosity index of the lubricating oil composition is preferably 270 or less, more preferably 260 or less, and further more preferably 250 or less in view of the good low-temperature viscosity characteristic.

The content of a boron element in the lubricating oil composition is preferably 180 ppm by mass or more, more preferably 190 ppm by mass or more, and further more preferably 200 ppm by mass or more on the basis of the total amount of the lubricating oil composition in view of the better corrosion protection of lead. The content of a boron element in the lubricating oil composition is preferably 440 ppm by mass or less, more preferably 420 ppm by mass or less, and further more preferably 400 ppm by mass or less on the basis of the total amount of the lubricating oil composition in view of the better corrosion protection of lead and fuel economy. The content of a boron element can be measured by the ICP-AES method.

The content of a calcium element in the lubricating oil composition is preferably 1800 ppm by mass or more, more preferably 1900 ppm by mass or more, and further more preferably 2000 ppm by mass or more on the basis of the total amount of the lubricating oil composition in view of the better corrosion protection of lead. The content of a calcium element in the lubricating oil composition is preferably 2700 ppm by mass or less, more preferably 2600 ppm by mass or less, and further more preferably 2500 ppm by mass or less on the basis of the total amount of the lubricating oil composition in view of the better corrosion protection of lead. The content of a calcium element can be measured by the ICP elemental analysis method.

The lubricating oil composition according to this embodiment is preferably used as a lubricating oil composition for an internal combustion engine. Examples of the internal-combustion engine include a gasoline engine, a diesel engine, an engine designed for fuel containing oxygen-containing compounds, and a gas engine. The lubricating oil composition according to this embodiment is particularly preferably used as a diesel engine oil.

Examples

Although the present invention will be described further more specifically on the basis of Examples hereinafter, the present invention is not limited to Examples.

Lubricating oil compositions each having a composition illustrated in Tables 1 and 2 were prepared by using a base oil and additives illustrated below.

(Base Oil)

-   Hydrorefined mineral oil (kinematic viscosity at 100° C.: 4.4 mm²/s;     and viscosity-index: 127)

(Additive)

-   A-1: Glycerin Monooleate -   A-2: Oleylamine -   A-3: Oleylamide -   a-1: Molybdenum Dithiocarbamate -   B-1: Boric Acid-Modified Polybutenyl Succinimide (weight average     molecular weight of polybutenyl group: 7420; and content of boron     element: 0.5% by mass) -   C-1: Calcium Salicylate Overbased with Calcium Borate (base number:     190 mg KOH/g; and content of calcium element: 6.8% by mass) -   D-1: Additive Package containing Calcium Salicylate, Calcium     Phenate, Dialkyldithiophosphate and the like. (content of boron     element: 0.12% by mass; and content of calcium element: 1.5% by     mass) -   E-1: Styrene-Diene Copolymer

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Composition (on the basis of the total amount of a lubricating oil composition) Base Oil Balance Balance Balance Balance Balance Additive A-1 % by mass 0.3 — — — — A-2 — 0.3 — — — A-3 — — 0.3 0.3 0.3 B-1 ppm by mass 117 117 117 117 153 (in terms of a boron element) C-1 ppm by mass 195 195 195 390 390 (in terms of a calcium element) D-1 % by mass 12.5 12.5 12.5 12.5 12.5 E-1 % by mass 6 6 6 6 6 Properties of a lubricating oil composition Kinematic mm²/s 10.0 10.0 10.1 10.0 10.1 viscosity at 100° C. Viscosity Index — 172 172 173 172 172

TABLE 2 Comparative Comparative Example 6 Example 7 Example 8 Example 1 Example 2 Composition (on the basis of the total amount of a lubricating oil composition) Base Oil Balance Balance Balance Balance Balance Additive A-3 % by mass 0.3 0.3 0.3 — — a-1 — — — — 0.3 B-1 ppm by mass 190 190 117 80 117 (in terms of a boron element) C-1 ppm by mass 390 195 — — 195 (in terms of a calcium element) D-1 % by mass 12.5 12.5 12.5 12.5 12.5 E-1 % by mass 6 6 6 6 6 Properties of a lubricating oil composition Kinematic mm²/s 10.1 10.2 10.1 10.0 10.1 viscosity at 100° C. Viscosity Index — 171 171 172 173 172

(Fuel Economy)

As to lubricating oil compositions of Examples 1 to 8 and Comparative Example 1, fuel economy was evaluated by friction coefficient by the SRV tester, and the HTHS viscosity at 100° C. (ASTM D4683). Results are shown in Table 3.

As to friction coefficient, a case where the friction coefficient was 0.150 or less was shown as “A”, a case where the friction coefficient was more than 0.150 and 0.155 or less was shown as “B”, and a case where friction coefficient was more than 0.155 was shown as “C”.

As to the HTHS viscosity at 100° C. (ASTM D4683), a case where the HTHS viscosity at 100° C. was 6.5 or less was shown as “A”, a case where the HTHS viscosity at 100° C. was more than 6.5 and 6.7 or less was shown as “B”, and a case where the HTHS viscosity at 100° C. was more than 6.7 was shown as “C”. The HTHS viscosity at 150° C. of all Examples and Comparative Examples were 2.9.

When both friction coefficient and the HTHS viscosity at 100° C. evaluated A or B, it can be said that the lubricating oil composition of the Example is good in fuel economy.

TABLE 3 Comparative Example Example 1 2 3 4 5 6 7 8 1 Fuel Friction B A A A A A B A C econ- coefficient omy HTHS A A A A A B B A A viscosity

(Prevention of Copper Corrosion)

As to the lubricating oil compositions of Examples 1 to 8 and Comparative Example 2, copper corrosion protection was evaluated on the basis of the high temperature corrosion bench test (JIS K2503: 2010). The test was conducted by the amount of a sample of 100 ml, the test temperature of 135° C., the test duration of 168 hours, the airflow rate of 5 L/h, and the catalyst of copper, lead or tin. Results are illustrated in Table 4. It can be said that a lubricating oil composition becomes good in copper corrosion protection as the amount of copper elution becomes small (for example, 20 ppm by mass or less).

TABLE 4 Comparative Example Example 1 2 3 4 5 6 7 8 2 Prevention of 3 4 3 4 5 3 4 2 22 copper corrosion (amount of copper eluted/ppm by mass)

(Prevention of Lead Corrosion)

As to the lubricating oil compositions of Examples 1 to 8, corrosion protection of lead was evaluated on the basis of the high temperature corrosion bench test (JIS K2503: 2010). Additionally, the condition was that the amount of a sample was 100 ml; the test temperature was 135° C.; the test duration was 168 hours; the airflow rate was 5 L/h; and the catalysts were copper, lead and tin. Results are illustrated in Table 5. It can be said that a lubricating oil composition becomes good in lead corrosion protection as the amount of lead elution becomes small (for example, 150 ppm by mass or less).

TABLE 5 Example 1 2 3 4 5 6 7 8 Prevention of lead 39 30 38 87 62 59 10 130 corrosion (amount of lead eluted/ppm by mass) 

1. A lubricating oil composition for an internal combustion engine, comprising: a lubricating base oil; an ashless friction modifier; and a boron-containing dispersant.
 2. The lubricating oil composition for the internal combustion engine according to claim 1, further comprising: an overbased organic acid metal salt overbased with calcium borate.
 3. The lubricating oil composition for the internal combustion engine according to claim 1, wherein the lubricating oil composition is a diesel engine oil. 